Document WO0006414 discloses such an articulation mechanism comprising:                a first end-plate,        a second end-plate mounted so as to pivot relative to the first end-plate about a main axis of rotation and comprising a ring gear,        a plurality of locking elements comprising at least a first locking element and a second locking element, each of the said locking elements comprising teeth capable of interacting with the teeth of the ring gear and being able to move between:                    an active position in which the teeth of each of the locking elements interact with the teeth of the ring gear, in order to prevent rotation between the first end-plate and the second end-plate about the main axis of rotation,            an inactive position in which the teeth of each of the locking elements are separated from the teeth of the ring gear, in order to allow rotation between the first end-plate and the second end-plate about the main axis of rotation,                        a cam that can be moved between a locked position in which it holds the locking elements in the active position and an unlocked position in which it allows the inactive position of the locking elements,        guide elements secured to the first end-plate and capable of guiding in rotation each of the locking elements relative to the first end-plate about a respective secondary axis of rotation parallel to the main axis of rotation,        a bearing surface secured to the second end-plate preventing the first locking element from being in the active position in a range of angular tilting positions of the first end-plate relative to the second end-plate.        